The present invention relates to jet pumps, which are commonly used to draw fuel from a main fuel tank chamber into a fuel pump reservoir to keep an adequate fuel supply in the fuel pump reservoir.
Fuel supply systems (sometimes called “fuel pump modules”) with jet pumps are designed to create a low pressure suction area by pushing fuel through a nozzle with a fuel supply pump. The low pressure suction area of the jet pump is in communication with the fuel in the main fuel tank so that the fuel from the main fuel tank is drawn into the suction area of the jet pump, mixing with the fuel exiting the nozzle in a mixing tube. The outlet of the jet pump discharges into the fuel pump reservoir to maintain an adequate fuel level for the fuel pump to supply to the engine, especially in the event of excessive lateral g-forces or sloshing due to harsh road conditions which may otherwise starve the fuel pump. Because conventional jet pumps deliver fuel from the main fuel tank to the fuel pump reservoir, often at or near the bottom of the fuel pump reservoir, a flow path is established whereby fuel has the potential to siphon out of the fuel pump reservoir back into the main fuel tank when the fuel pump is turned off. This “dry” condition creates a problem for reliability as a lack of fuel in the fuel pump reservoir will hinder or completely prevent proper re-starting of the fuel pump and also the jet pump. Typically, the solution to prevent unwanted siphoning involves the addition of a check valve in the jet pump flow path between the main fuel tank to the fuel pump reservoir, so that fuel can only flow from the main fuel tank into the fuel pump reservoir and not vice versa. However, this presents the need for additional components and cost, and also can have a significant effect on the efficiency of the jet pump, whereby energy is wasted to overcome the resistance presented by the check valve.